1. Field of the Invention
This invention relates to a radiographic intensifying screen (hereinafter referred to as "intensifying screen"), and more particularly to an intensifying screen exhibiting improved physical properties in which a radioluminescent phosphor is dispersed in a binder comprising linear polyester resin or linear polyester resin crosslinked with a crosslinking agent to form a fluorescent layer.
2. Description of the Prior Art
In radiography such as medical radiography used for medical diagnosis and industrial radiography used for nondestructive inspection of industrial materials, an intensifying screen is used in face contact with a radiographic film to increase the sensitivity of the radiographing system.
The intensifying screen comprises a substrate and a fluorescent layer provided thereon. The fluorescent layer comprises a binder and a phosphor which emits light of high luminance by the excitation of radiation such as X-rays (radioluminescent phosphor) dispersed in the binder. Usually, the naked surface of the fluorescent layer is covered with a transparent protective layer. Some intensifying screens have a light-reflecting layer or a light-absorbing layer between the substrate and the fluorescent layer. Further, some intensifying screens used for nondestructive inspection of industrial materials have a metallic foil between the substrate and the fluorescent layer.
The intensifying screen having the above-mentioned structure is generally prepared by the following manufacturing process.
A radioluminescent phosphor is mixed with a binder in a suitable mixing ratio using a suitable solvent to prepare a dispersion in which the radioluminescent phosphor is dispersed in a solution of the binder. Then, the dispersion thus obtained is uniformly applied to a substrate by means of a doctor blade, a roll coater, a knife coater, or the like and dried to form a fluorescent layer. In the preparation of the intensifying screen having a light-reflecting layer, a light-absorbing layer or a metallic foil between the substrate and the fluorescent layer, the light-reflecting layer, the light-absorbing layer or the metallic foil is provided on the substrate beforehand, and then the dispersion is applied thereto and dried to form the fluorescent layer. After the formation of the fluorescent layer, a transparent protective layer for protecting the fluorescent layer is generally provided on the fluorescent layer. Unless otherwise indicated, the term "substrate" as used herein also means a substrate on one surface of which the light-reflecting layer, the light-absorbing layer or the metallic foil is provided beforehand.
From the viewpoint of practical use, it is desired for the intensifying screen to have a high flexing resistance and a high adhesion of fluorescent layer to substrate. That is, the fluorescent layer of the intensifying screen should not readily craze and peel off from the substrate when the panel is bent.
In the conventional intensifying screen, cellulose derivatives such as nitrocellulose and cellulose acetate have been practically used as the binder of the fluorescent layer of the screen. In the dispersion for forming the fluorescent layer of the intensifying screen prepared using cellulose derivative, the radioluminescent phosphor is dispersed uniformly. However, the intensifying screen prepared by using the dispersion exhibits low performance in flexing resistance and adhesive force of fluorescent layer to substrate. Accordingly, the fluorescent layer of the screen readily crazes and peels off from the substrate when the panel is bended.
As described above, the intensifying screen in which cellulose derivative is used as the binder of the fluorescent layer exhibits low performance in flexing resistance and adhesion of fluorescent layer to substrate. Accordingly, an intensifying screen exhibiting higher performance in flexing resistance and adhesion of fluorescent layer to substrate than the intensifying screen in which cellulose derivative is used as the binder of the fluorescent layer is desired.